Damage behavior of Nb3Sn/Cu superconducting strand at room temperature under asymmetric strain cycling

• Published in: Fusion engineering and design Vol. 172; p. 112869
• Main Authors: Jiang, Lang, Su, Xiyang, Shen, Liuyang, Zhou, Jun, Zhang, Xingyi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2021; Elsevier Science Ltd
• Subjects: Accumulated plastic strain; Asymmetric strain cycling; Asymmetry; Cycles; Damage assessment; Damage evolution; Degeneration; Degradation; Evolution; Fatigue life; Fatigue tests; Mathematical models; Plastic deformation; Room temperature; Stiffness; Stiffness degradation; Strain analysis; Strands; Superconductivity; Accumulated plastic strain; Fatigue life; Damage evolution; Asymmetric strain cycling; Stiffness degradation
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2021.112869

•An analytical model was proposed to study the effects of strain range and strain peak on stiffness degeneration, accumulated plastic strain, and fatigue life in the Nb3Sn/Cu superconducting strand under asymmetric strain cycling.•There are three different stages during the damage evolution in the fiber-matrix composites under strain fatigue.•The analytical model is in good agreement with the experimental results under asymmetric strain cycling.•Nb3Sn sub-elements begin to damage and break seriously in no more than 5000 cycles, and the damage of the Cu matrix mainly occurs at the end of the fatigue life. In this study, damage evolution of Nb3Sn/Cu superconducting strand was investigated under asymmetric strain cycling. The results of the fatigue tests indicate that higher strain ranges and peaks can accelerate damage evolution, and damage evolution occurs seriously at the early fatigue stage. Based on the stiffness degradation rule of composites, two independent plastic damage evolution equations of the Nb3Sn sub-elements and Cu matrix were derived to obtain stiffness degradation and fatigue life by considering the effect of strain range and strain peak, respectively, and the accumulated plastic strain of Nb3Sn/Cu superconducting strands was obtained by deriving the total damage evolution equation. The proposed model was verified and validated by studying the fatigue behavior of Nb3Sn/Cu superconducting strands under asymmetric strain cycling. A good agreement between the analytical model and experimental data irrespective of the strain range and strain peak shows that the analytical model can not only predict the stiffness degeneration and accumulated plastic strain, but also describe the fatigue life of Nb3Sn/Cu superconducting strands under asymmetric strain cycling.